This invention relates to absorbent composites having improved multifunctional absorbent properties useful in absorbent articles. More specifically this invention relates to absorbent composites having rapid fluid intake and rapid lock-up of liquid.
Various absorbent materials and structures are known in the art. Important characteristics of commercial absorbent materials and structures include either a high rate of fluid intake or rapid lock-up of liquid, but not both. Nonwoven surge materials, as taught in U.S. Pat. No. 5,490,846 to Ellis et al. and in U.S. Pat. No. 5,364,382 to Latimer, for example, have excellent intake functionality but typically almost no fluid retention properties. Current commercial diaper absorbent cores comprising an absorbent fluff and superabsorbent material combination typically provide good fluid absorbency but, often depending on the core density, typically poor fluid intake.
High liquid intake rate composites can be achieved through a variety of ways. High stiffness superabsorbent particles, high stiffness fibers, and/or stabilization of the composite structure have been shown to be effective at achieving high intake rates and sometimes maintaining that rate over multiple insults. However, swelling kinetics of the superabsorbent particles that dictate the speed of liquid lock-up into the superabsorbent particles are typically inadequate.
A typical disposable absorbent product generally has a composite structure including a topsheet, a backsheet, and an absorbent structure between the topsheet and backsheet. In current commercial absorbent structures layers of different materials, such as a surge layer and an absorbent core layer, are required to provide desired fluid handling characteristics of high liquid intake and high liquid lock-up. The result may be an absorbent article with many production steps and high cost. There is a need for an absorbent composite having enhanced fluid intake and high liquid lock-up characteristics that could be used alone or in combination with other materials in an absorbent article.
This invention is directed to absorbent composites having improved fluid handling properties and methods of making the absorbent fibrous or non-fibrous structure. The absorbent fibrous composites of this invention have a high intake rate of liquid and a high liquid lock-up fraction. Absorbent composites of this invention can be any foam, foam-like composite, airlaid composite, airformed composite, wetformed composite, or combinations thereof. Absorbent composites of this invention can be modified using treatments such as ultraviolet radiation, ultrasonic, microwave radiation, and/or in-situ polymerization treatment to enhance liquid intake and lock-up performance.
In one embodiment of the invention, the absorbent composite includes a freeze-dried absorbent composite. The absorbent composite is made by forming a slurry comprising a water-insoluble fiber, and a binding agent. An absorbent material is then added to the slurry. The solution is cooled to a temperature between about xe2x88x9250xc2x0 C. and 0xc2x0 C. at a cooling rate effective to freeze the water. The frozen water is removed through sublimation and a fibrous absorbent composite is recovered. The freeze-dried composites of this invention have an intake rate of at least about 1.9 cubic centimeters (cc) of liquid/second at 80% composite saturation and a liquid lock-up fraction of at least about 0.70 at 50% superabsorbent saturation, as determined by test procedures described below.
In one embodiment of this invention, the absorbent composite includes an airformed absorbent composite. The airformed composite is formed by mixing superabsorbent material and a fibrous material and using an airforming machine to lay down a web of intermingled fibers and superabsorbent materials onto a porous tissue. The airformed absorbent composites of this invention have an intake rate of at least about 1.9 cc liquid/second at 80% absorbent composite saturation and a liquid lock-up fraction of at least about 0.70 at 50% superabsorbent saturation, as determined by test procedures described below.
In another embodiment of this invention, the absorbent composite is formed from a non-fibrous matrix. The non-fibrous absorbent composites of this invention have an intake rate of at least about 1.9 cc liquid/second at 80% absorbent composite saturation and a liquid lock-up fraction of at least about 0.70 at 50% superabsorbent saturation, as determined by test procedures described below.
Binding agents can be used in absorbent composites of this invention to provide strength to the absorbent composite structure both in the dry state and the wet state. Binding agents are water-insoluble in the absorbent composite and can bind the fibers of the absorbent composite together. Binding agents can be water-swellable and can be used to enhance liquid intake and liquid lock-up. A crosslinking agent may be needed to insolubilize a water-soluble binding agent after formation of the absorbent composite.